Automatic telephone system



C. E. LOMAX E' AL AUTOMATIC TELEPHONE SYSTEM Oct. 23, 1928.

Inuen are I Zarance EL max and Norman H. Saunders Oct. 23, 1928.1,688,588

- c. E. LOMAX ET AL AUTOMATIC TELEPHONE SYSTEM Fil y 1927 s Sheets-Sheet'2 Oct. 23, 1928.

C. E. LOMAX El AL.

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C. E. LOMAX ET AL,

AUTOMATIC V TELEPHONE SYSTEM Filed July 2, 1927 a Sheets-Sheet "4 InuenDr's- I Zar EL'LGB ELumax and N urman HEaundars Oct. 23, .1928.

C. E. LOMAX ET AL AUTOMATIC TELEPHONE SYSTEM 1,688,588 C. E. LOMAX ET ALAUTOMATIC TELEPHONE SYSTEM Oct, 23, 1928'.

iled July 2, 1927 8 e Sheets-Sheot '6 Inuanlfi Clarence ELumax andNorman Hia unfiars Patented Oct. 23, 1928.

UNITED STATES 1,688,588 PATENT OFFICE.

CLARENCE E. LOMAX OF OAK PARK, AND NORMAN H. SAUNDERS, OF HOMEWOOD,ILLI- NOIS, ASSIGNORS TO RESERVE HOLDING COMPANY, OF KANSAS CITY,MISSOURI, A

CORPORATION OF DELAWARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed July 2,

The present invention relates in general to automatic telephone systemsmore partlcularly to such systems in which line finders are employed toconnect an idle selecting switch witha calling line; and the prlncipalob ect of the invention; briefly stated, is the production of a new andimproved finder switch system, the improvements tending to make thesystem more reliable, to give uniform high quality service, and to makeit cheaper to install and maintain.

As afurther object of our invention we provide a new and improvedcircuit for simultaneously testing two sets of contacts, the improvementinsuring a positive stopping on a set of contacts if one of the lines ofthe set is calling even though the other is now calling.

As a further object, we provide a new and improved preferential servicearrangement, which insures uniform service to all of the subscribers ofa line group under all conditions of traflic in the group.

Further objects, not specifically mentioned here will best be understoodfrom reading the detailed description and claims which follow.

The drawings comprising Figs. 1 to 6 inclusive when arranged with Figs.1, 2 and 3 from left to right in a straight line, with Figs. 4, 5, and6, placed directly beneath, and with correspondingly numbered lines inalignment, show sufiicient details to enable a clear understanding ofour invention.

Referring now to Fig. l in more detail, we show a finder FA, and aselector EA, the selector being the old and well known type of Strowgerselector, forms no integral part of the present invention being shownmerely to enable a clearer understanding of the operation of the system.The finder switch FA, is of the Strowger vertical and rotary type, whosewipers 230 to 235 inclusive, are moved first in a vertical direction andthen in a rotary direction to select the contacts of a call- 1927.Serial No. 208,059.

which sweeps over the bank VA to determine the number of digits to bedelivered to the vertical magnet of the finder.

In Fig. 2 we show subscribers lines S and S, it being assumed for thepurpose of illustration that subscribers line S is line number 125, andsubscribers line S is line number 295. Associated with each line are theusual line and cut-ofi relays, the circuits of which have been modifiedin accordance with the objects of the present invention. In Fig. 2 wealso show the vertical banks VA and VB, which together with the wipers262 and 263 determine the vertical designation to which the finderswitches are to be sent.

In Fig. 3 we show finder F13 and the selector 'EB, the switches beingduplicates of those shown in Fig. 1 need not be explained in detail atthis time.

In Fig. 4, we show the finder allotter comprising magnet 401 and wipers4:11 to 415 inclusive. thru which the finders of group A, that is thegroup containing finder FA, are allotted for use one at a time.Associated with the finder allotter are the control relays 102 to 405,the purpose of which will be best understood from the detaileddescription which follows.

In Fig. 5 we show the control keys K1 and K2, thru the operation ofwhich the switch room attendant may cut out a group of finders, anddirect all the traffic in the exchange to the other group of finders, incase of a fault in either group.

In Fig. 6 we show a finder allotter comprising wipers 605 to 609inclusive, and associated relays 601 to 604;, which equivalentis aduplicate of that shown in Fig. 1, and thru which equipment the findersof the B group, con taining finder FB, are allotted for use one at atime.

Throughout the drawings, we have shown a plurality of batteries to avoidunnecessary complication- In an actual installation there would be butone battery, preferably with its positive pole grounded.

In order to enable a clear understanding of the invention it will now beassumed that the subscriber S initiates a call, and it will be furtherassumed that the group of finders containing finder FA is in readinessto handle the call. Responsive to the removal of the receiver from theswitch hook at the substation S, line relay 201 associated with the lineS is energized, to mark that line busy in the connector bank to preventintrusion on the call by a connection, to mark the line calling in thefinder bank to render it se- 7 lectable by the finder, and to placeground tact of the bank VA, will cause the finder FA' upon the startconductor to start the finder equipment in search of the calling line.The energization of the line relay 201 places the ground upon the levelmarking conductor 250, which is connected to the second contact in thebank VA, also thru the resistance 251 and the conductor 260 to the startrelay 105 associated with the finder allotter shown in Fig. 4. Since thecalling line S has a finder bank designation of 125 and since thepresent call is assumed to be handled by the finder group to which thatline is first choice, it

will be necessary for the finder to take two vertical steps to reach thelevel containing the calling line. The placing of ground on conductor250 and the consequent marking of ground potential on the second bankconto stop on the second level, at which time its wipers will be rotatedinto that level to pick out the contacts of the line S. Since the finderFA is a 200 point finder, it is equipped with two sets of wipers, asmentioned hereinbefore. When the wipers are rotated into the level,tests will be made simultaneously by both sets of wipers, that is if thefinder is elevated to the second level, and steps into the first contactin that level, the lower set of wipers comprising wipers 233 to 235 willtest the line upon which they are resting, in this case line 121, and atthe same time the upper set of wipers comprising wipers 230 to 232inclusive will test the line upon which they are resting, in this caseline 221, and if neither one of these lines are calling, both sets ofwipers will he stepped on to the next contact, where the test will berepeated.

When the line S is encountered, the absence of ground potential on thetest contact associated with that line will render it selectable,causing the finder FA to stop thereon and switch thru, so that thecalling line will be connected thru to the selector EA, the connectioncontaining no bridges across line, g fgier at the line equipment or atthe finder Referring now to the finder more in detail, responsive to theplacing of ground upon the conductor 250, and the consequentenergization of the start relay associated with the finder allotter,start relay 107 of the finder is energized, over a circuit includingcontacts on both the vertical magnet 105 and the rotary magnet 10 1, andupon energizing relay 107 closes the circuit for the vertical magnet 105which energizes and opens the circuit of relay 107, in addition toelevating the wipers of the switch one vertical step. The deenergizationof relay 107, opens the circuit of vertical magnet 105, causing thatmagnet to fall back and again close the circuit of relay 107, thisintermittent operation of the magnet and relay continuing as long as thevertical Wiper 202 of the finder FA encounters battery potential. Whenthe level containing the calling line is reached, in this case thesecond level, a ground potential picked up by the wiper 262, energizesthe relay 106 in addition to holding the relay 107 energized, so thatwhen the vertical magnet opens the circuit of relay 107, that relay doesnot fall back but is maintained energized over the substitute circuit.The energization of relay 106 transfers the circuit closed by relay 107from the vertical magnet to the rotary magnet 104, and since the relay107 is in its energized position at the time this transfer is made, therotary magnet immediat-ely receives an impulse, and energizes to rotatethe wipers one step. The rotary magnet upon energizing, opens thecircuit of the relay 107, at a point which also opens the circuit fromthe vertical wiper 262, permitting the relay 107 to fall back to end thepulse. When the wipers are advanced to the first contact of the level,the first test wiper will pick up a ground, provided the line is notcalling, said ground completing a circuit to energize the relay 109,which energizes and transfers the testing circuit to the other set ofwipers on the switch. If the other line now engaged by the wipers, isnot calling, the other test wiper will pick up another ground, whichcompletes a circuit to again energize with relay 107, to step the wipersof the switch onto the next set of contacts. Thus it will be seen thatthe changeover from vertical to rotary motion is ac complishedpositively, without any delay, and that the stepping of the switch in arotary direction is dependent upon the presence of ground upon thecontacts engaged by both of the test wipers.

Assume now that at the time the sub-station S initiated the call, all ofthe finders in the group containing finder FA, are busy, in which casethe call will be handled by a finder in the group containing finder FB,provided no calls from lines to which that finder is first choice are inprogress at the time. It will be noted that the placing of ground onconductor 250 and the contact 2 of the vertical bank VA also placesground upon the contact 9 of the vertical bank VB. It will also beremembered that the banks of the finders are slipped between the groupsA and B, so that the lines appearing in the lower half of the banks ofgroup A appear in the upper half of the banks of group B. Responsive tothe grounding of the conductor 250, the start rclay 405 will beenergized, and since it is now assumed that all of the finders in thegroup A are busy, that relay starts a finder in group B, for examplefinder FB, which operates in presence of ground upon the contactsengaged y the test wipers of both sets. The operation of the finder FBis identical with that of the finder FA, and need not be explained indetail at this time.

From the foregoing it will be seen that normally calls from the line Sare handled by the finder FA, and that in case all the finders in thegroup A are busy, calls from a line such as S can be handled by thefinder FB.

In a similar manner calls from the line S has as its first choice thefinder FB, in which finder it appears in the second level, so that thewipers of FB are moved vertically two steps to engage the level.containing the calling line S1. If, however, the group containing thefinder FB is busy at the time that Fl makes a call, that call will startthe finder FA, provided there are no calls pending in that group at thetime, and the line S1 will be picked up b the finder FA, which at thistime must ta re nine vertical steps to reach the level containing theline. It will be noted that the second bank contact in the vertical bankVB is multipled to the 9th bank contact to the vertical bank VA, so thatwhen the conductor 252 is grounded responsive to the energization to theline relay by the initiation of a call on the line S1, level 2 of thebank VB and level 9 of the bank VA are marked calling, so that whicheverfinder is started to pick up the call will stop on the proper level whenreached.

In the normal operation of this system, the finder allotter DA does nothave access to the finders of the group B, and similarly the finderallotter DB does not have access tothe finders of the group A. It mayhappen howeverthat because of a fault in one or the other of the controlequipments, it is necessary for the dispatcher to cut that equipment outof service for an appreciably long time, during which it will benecessary to employ both groups of finder switches, under the control ofone of the finder allotters. Accordingly, the finders of group A, inaddition to being multipled into the first half of the bank of thefinder allotter DA, are multipled into the last half of the bank of thefinder allotter DB, so that when the key K1 is thrown, finder allotterDB may have access to the finders of the group A. Similarly finders ofthe group B in addition to being multipled intothe first half of thebanks of the finder allotter DB, are multipled into the second half ofthe banks energizing the relay 405.

of the finder allotter DA, so that when, the

key K2 is thrown to cut DB out of service,

finder allotters DA will have access to the finders of the group B. Inorder to avoid an L I unnecessary complication of the drawings,

these multiple connections have not been shown, since they willbe-understood and appreciated by one skilled in the art from-theforegoing brief description.

Having thus described our invention in general, we will now proceed withadetailed description of its operation:

.Line S initiates a call;

Relay 201 also closes at spring 213 and its make contact a circuit fromground thru that spring and springs 214 to the start conductor 250,thereby placing ground potential upon the second bank contact ofvertical bank A, and upon theninth bank contact of the vertical bank VB,for a purpose which will be brought out hereinafter. Ground placed uponconductor 250 by the springs 213 of the relay 201, also completes acircuit thru the resistance 251, conductor 260, thru springs 501 of thekey K1, conductor 43?, thru the winding of relay 405 to battery, Relay405 upon energizing, closes a circuit from ground thru springs 429,spring 426 and its make contact, springs 422, thru the winding of relay402, thru spring 427 and its make contact conductor 445, interruptivesprings 410, thru the winding of magnet 401 to battery. Relay 402energizes over this circuit, but because of the high resistance of thewinding of the relay 402, magnet 401 does not energize at this time. Theenergization of relay 402 prepares'the start circuit, to start thefinder FA, in search of the calling line S.

The first vertical step.

The energization of relay 402, at springs 417 closes a holding circuitfor the all finders busy relay 404, to prevent that relay deenergizingwhen the finder FA moves oii'nor mal, it that finder should happen to bethe last idle finder of the group. Relay 402 at springs 416 opens apoint in the circuit of the relay 602 of the finder distributor DB, theopening of that circuit being without particular effect at this time.Relay 402 at springs 420 opens a point in the test circuit of the finderallotter DA, to prevent that allotter searching for an idle finder atthis time. Relay 402 at springs 418 closes a circuit from ground thruthose springs, conductor 446, wiper 411 now engaging the contact towhich conductor 162 is connected, spring 125 and its break contact,spring 12.1, springs 120, thru the winding of relay 107 to battery,energizing the relay 107. Relay 107 upon energizing closes a circuitfrom grounded conductor 162, thru springs 129, spring 124 and its breakcontact, thru the winding of the vertical magnet 105 to battery,energizing the vertical magnet which elevates the shaft containingwipers 230 to 235 inclusive one vertical step, and bringing the verticalwiper 262 into engagement with its first bank contact. The energizationof the vertical magnet 105 opens the circuit of relay 107 at springs121, permitting that relay to fall back to open the circuit of thevertical magnet at springs 129. This interaction of relay 107 and thevertical magnet 105' will continue until the wiper 262 encounters agrounded contact, the continuation of this action operating the verticalmagnet to elevate the shaft containing the wipers of the finder FA in avertical direction a number of steps depending upon the number ofenergizations of the magnet 105. When the vertical magnet 105 isenergized and springs 121 are open, circuit may be traced from groundedconductor 250 to resistances 251 and 251 in series, vertical wiper 262,conductor 158, thru the upper winding of relay 106, thru springs 120,thru the winding of relay 107 to battery. Because of the high resistanceof the resistances 251 and 251 in series, this circuit is ineffectiveeither to energize relay 106 or to hold the relay 107 in its energizedposition.

The last vertical step.

Since the calling line has a finder bank number of 125, it appears inthe second level of the banks of the finder FA, and consequently, whenthe vertical magnet 105 has energized the second time, to elevate thewipers of the switch FA opposite the second level of the bank and thevertical wiper 262 into engagement with its second bank contact, theswitch over circuit will be completed when the magnet 105 is energizedand the springs 121 broken. At this time the wiper 262 engages directground potential from the conductor 250 and the second bank contact,completing a circuit thru the wiper 262, conductor 158, upper winding ofrelay 106, springs 120, thru the winding of relay 107 to battery. Thiscircuit will be-completed as soon as the vertical magnet 105 hasenergized sufficiently to move the wiper 262 into an engagement with thesecond bank contact. The circuit will. therefore, be completed prior tothe opening of springs 121, so that the opening of those springs willnot open the circuit of relay 107, it being maintained energized fromthe ground on conductor 158 as explained above. As soon as the springs121 are open, relay 106 energizes, locking itself through its lowerwinding and spring 123 to the grounded conductor 162, independent of theenergizing circuit thru its upper winding. The energization of relay 106opens the circuit of magnet125, which at this time has completed itsstroke and opened springs 121, and closes in its place a circuit for therotary magnet 104, energizing that magnet immediately from ground onconductor 162 thru the springs 120, spring 124 in its make contact thruthe winding of the magnet to battery. The energization of rotary magnet104 rotates the wipers, 230 to 235 inclusive, one rotary step intoengagement with the first contact of the second level of their banks.The rotation of the shaft also disengages wiper 262 from its verticalbank, that disengagen'ient being without effect at this time since relay106 is maintained energized independent of the circuit thru that wiper.The energization of rotary magnet 104 opens at springs 120 the circuitof relay 107, permitting that relay to fall back and open the circuit ofthe rotary magnet of springs 129. The interaction of relay 107 andmagnet 105, having completed the first rotary step, has positioned thewipers of the finder FA onto the first bank contact, in which positionthey are prepared to determine whether or not the first line in thelevel is a calling line.

Rotary testing.

It will be noted that the line equipment comprlsing relays 201 and 202for the line S and 203 and 204 for the line S1, normally places a groundupon the private contacts associated with that line in the finder bank,at springs 213 and 218 respectively, so that if the line is in anuncalling position, that is with its line relay 201 or 203 normal, the

private contact will be maintained at ground potential. When the wiperset 230 to 232 engage its bank contacts, the private wiper 231, willencounter ground potential if the first line in the level happens to bean uncalling line, as it is assumed to be in this case. Similarly thewiper set 233 to 235 inclusive, will be positioned on the first contactif its banks, and private wiper 234 will encounter a ground potentialif-the first line of the level is not calling. Since it is assumed thatthe line S, which is the calling line in the present case, has a finderbank number of 125, it will be necessary for the wipers to be rotatedfive steps to encounter the contacts of the line. The positioning ofwiper 234 upon the first private contact of its bank, closes a circuitfrom ground on that contact, thru the wiper, conductor 157, thru springs122, thru the normally closed contacts controlled by spring 132, thruthe lower half of the winding of relay 109 to battery, energizing thatrelay which at springs 137 and 141 transfers the talking conductors fromthe lower to the upper set of wipers, this transfer-being withoutparticular effect at this time. At spring 139, relay 109, prepares alocking circu1t for itself, that circuit being held open at the time byspring 132 of the relay 108. At spr ngs 138, relay 109 connects theupper test wiper 231, thereby closing a circuit from the groundedcontact upon which that wiper 1s now restin thru conductor 156, spring138 and its mzfke contact, thru spring 131 and its break contact, thruspring 125 and its make contact, thru springs 121, springs 120, thru thewinding of relay 107 to battery. Re-

lay 107 energizes over this circuit, closing the circuit to the rotarymagnet 104 as before, energizing that magnet to advance the Wipersanother step and to open the circuit of relay 107 and springs 120. Aslong as wipers 231 and 234 encounter grounded contacts, relays 109 and107 will be energized, the former to shift from one wiper set to theother and the latter to close the circuit of the rotary magnetpreparatory to taking another step. It should also be noted that whilethe wipers 231 and 234 are engaging grounded contacts, switch thru relay108 is short circuited, having ground from release trunk conductor 151connected to its upper terminal, and having ground from wiper 234connected to its lower terminal over a circuit thru conductor 157,spring 128, during the interval that relay 107 is deenergized, thruspring 138 and its break contact spring 131 and its break con tact, tothe lower terminal of relay 108. When relay 109 has energized,preparatory to energizing relay 107, relay 108 is short circuited fromwiper 231, over conductor 156, spring 138 and its make contact, spring131 and its break contact, to the lower terminal of the relay 108. Itshould also be noted that when the wiper 234 passes over ,a plurality ofcontacts all of which are grounded, that Wiper bridges from one groundedcontact to another during its move ment, and the circuit of relay 109is, therefore, maintained, so that that relay does not fall back at eachstep. However, relay 107, whose circuit is opened at springs 120, fallsback at each step so that the stepping action of the finder FA in arotary direction is dependent upon the finding of ground upon both ofthe private wipers. In the instant call since the line S is assumed tobe finder bank number 125, five rotary steps will be taken by the finderFA to connect with the calling line, each step being a duplicate of theone just described need not be repeated at this time.

Finder FA switches through. At the end of the said five steps, when thewipers 233 to 235 engage the bank contacts to which conductors 254, 255and 256 are attached, the circuit of relay 107 is opened atspring 120,that relay falls back to the ends of pulse. Since wiper 234 now an agesan ungrounded contact, the circuit 0 109 is opened, permitting thatrelay to fall back. The deenergization. oflrelay 109 prevents a furthercnergization of relay 107, even though the. upper test wiper 231 may beengaging a grounded contact at the moment. As soon as rela 109 fallsback, the short circult is remove from the windin of switch thru relay108, that relay energizes over a circuit traceable from ground on spring113 of the release relay of the selector EA, release trunk conductor151, through the winding of switch thru relay 108, through spring 125and its make contact, spring 121, springs 120, relay 107 having fallenback and opened the circuit of the rotary magnet to permit that magnetto fall back, through the winding of relay 107 to battery. Relay 108energizes in the circuit, however, because of the high resistance of thewinding of relay 108 relay 107 does not energize. Relay 108 uponenergizing, switches thru the finder, connecting the selector EA to thecalling line S, over a circuit traceable from ground to the lowerwinding of line relay 102, thru spring 119 and its break contact,conductor 153, springs 136, spring 141 and its break contact, conductor160, wiper 235, conductor 255, thru the substation S, conductor 254,wiper 233, conductor 154, through spring 137 and its break contact,springs 130, conductor 150, spring 117 and its break contact, throughthe upper winding of the line relay l02tto battery. At springs 131,relay 108 connects the release trunk conductor 151 through the normallyclosed contact controlled by spring 138, through springs 128, conductor157, wiper 234, now engaging conductor 256, through the springs 212, theleft hand winding of relay 201, through the winding relay 202 tobattery. The ground placed upon release trunk conductor 151 by thesprings 113, completes the circuit for relay-s 201 and 202, the latterto energize and remove all attachments from the calling line S, and theformer to be maintained energized by its left hand winding. The callingsubscriber now has a clear line throu h from his substation to theselector EA, being audible to him over a circuit connected in the groundside of the lower winding of relay 102, this call tone generator beingold and well known to those skilled in the art is ial tone not shown inthe drawings. The calling sub- Finder allotter DA seeks another finder.

Returning now to the energization of switch through relay 108 of thefinder FA, the closing of springs 135 places a ground through thosesprings to conductor 164, through the wiper 413 now engaging thatconductor, conductor 448, thru the winding of relay 403 to battery,energizing the relay 403. Relay 403, upon operating springs 421,d1sconnects the ground placed on the negative line conductor 150 throughthose springs and resistance 450, to permit the calling subscriber tomanipulate his calling device and operate the selector. Relay 403, atspr1ngs 422, opens a previously traced circuit for relay 402, permittingthat relay to fallback. At springs 423, relay 403 opens a pomtan thesupervisory circuit, permitting the signals controlled thereby torestore to normal. The deenergization of relay 402, at spr1ngs 418removes ground from the conductor 162, thereby releasing the relay 106,of the finder FA, which was locked thereto through springs 123. Thedeenergization of relay 402 closes springs 420, thereby completing thecircuit from ground through olf-normal spring 140 of the finderconductor 165, wiper 415 now engaging that conductor, conductor 432,springs 420, conductor 449, springs 427, conductor 445, interruptersprings 410, through the winding of the rotary magnet 401 to battery,energizing this magnet, preparatory to advancing the wipers 411 to 415of the finder allotter DA one step. Magnet 401 upon energizing opens itsown circuit at interrupter springs 410, and falls back to advance thewipers onto the next bank contact. If the next finder of the group isbusy, wiper 415 Will again encounter a grounded contact, and the abovetraced circuit will again be completed, the magnet operating to advancethe wipers another step. The magnet 401 will therefore operate in abuzzer like fashion as long as the wiper 415 engages grounded contacts,coming to rest upon the first ungrounded contact, which is associatedwith the first idle finder of the group. I

All finders busy in group A.

, relay 404 is maintained energized normally over circuits traceablefrom ground at springs 115 of the selector EA, springs 116 and 114 andtheir respective break contacts, conductor 152, off normal springs 126,conductor 161, normally closed contacts 502 of the key K1, conductor436, springs 425, through the winding of relay 404 to battery.

When the selector EA and the finder FA were taken for use, this circuitis opened at springs 116 of the line relay 102 of the selector, andlater opened again at ofi' normal springs 126 when the finder is movedout of its normal position. Relay 404 is maintained energized during thesetting of the call by the ground placed on conductor 435 by springs 417of relay 402. When the relay 402 falls back after the finder FA hasswitched thru, the circuit of relay 404 istherefore opened, permittingthat relay to fall back. The deenergization of relay 404, at springs 426extends the start circuit away from relay 402 and towards relay 604 ofthe group B, so that if the start relay 405 is energized group B relay604 will be energized in the manner described hereinafter. Thedeenergization of relay 404 at springs 427 opens a point in the testingcircuit of the finder allotter DA, so that if wiper 415 is standing on agrounded contact, the magnet 401 is not energized, since there would beno object gained by moving the wipers of the allotter DA at this time.The deenergization of relay 404 closes spring 428 and its break contact,closing the obvious circuit for the magnet 407 of the meter to recordthat an all trunks busy condition exists in group A. With an all trunksbusy condition existing in the group A, calls originating therein willbe handled by the group B control equipment and finders, in a mannerwhich will be pointed out in detail hereinafter. As soon as one of thefinder selector links of the group A becomes idle, the above tracedcircuit for relay 404 will be closed, energizing that relay, to closethe testing circuit of the finder allotter DA, thereby operating thatallotter to pick out the idle finder, in a manner which has beenhereinbefore pointed out.

. The foregoing description shows how a call originating in the grou Ais handled by the group A control equipment and finders, and a call willnow be traced thru the group B control equipment.

Line 8 initiates a call.

sociated with line S in the finder banks, and

closes the circuit thru the make contact of spring 218 and springs 219to conductor 252. This ground on conductor 252 places ground potentialupon the second bank contact of the vertical bank VB of the finder FE,and also upon the ninth bank contact of the bank VA of, the finder FA.The ground on conductor' 252 completes a circuit thru resistcontact,spring 622 and its break contact,

springs 628, through the winding of relay 604 through springs 623,through the interrupter springs 611, through the winding of the magnet610 to battery. Relay 604 energizes over the circuit, but because of theresistance of that relay, magnet 610 is prevented from energizing.

Vertical impulsing.

The energization of relay 604 closes a circuit from spring 633,conductor 639, wiper 609, conductor 37 6, spring 338 and its breakcontact, springs 350, springs 349, conductor 370, through the winding ofrelay 303 to negative battery. Relay 303 energizes, and at spring 334closes a circuit from grounded conductor 37 6, spring 337 and its breakcontact through the winding of vertical magnet 306 to battery. Verticalmagnet 306, energizes, elevating the wipers 236 to 241 inclusive andvertical wiper 263 one step, the former wipers standing opposite thefirst level and the latter wiper engaging the first contact of its bank,and at the end of the energization of magnet 306, interrupter springs350 are opened, to open the circuit of relay 303, which falls backopening springs 334 to open the circuit of the vertical magnet. Verticalmagnet 306 and the relay 303 interact in this manner until the verticalwiper 263 encounters ground, which in this case will be at the end ofthe second impulse.

Switch over to rotary.

After the vertical magnet has elevated the shaft containing the wipers,two steps, to bring the vertical wiper 263 into engagement with thesecond bank contact, the circuit for relay 304 is completed from groundon conduetor 252 now engaged by thewiper 263, conductor 364, through theupper winding of relay 304, through the. rotary interrupter springs 349,through the winding of relay 303, maintaining that relay energizedindependent of the interrupter springs 350. Relay 304 energizes over theabove circuit, transferring the circuit through springs 337 from thevertical magnet 306 to the rotary magnet 305, and locks itself togrounded conductor 376 at spring 336. The rotary magnet 304 is energizedover this circuit to rotate the wipers one rotary step into engagementwith the first contact set in the selected level.

Rotarg testing.

Since the calling line S is assumed to be number 295, five rotary stepsmust be taken before the wipers engage the contacts of that line. Whenthe wipers are advanced to the first contacts of the selected level,private wiper 240 of the lower wiper set encounters "round, completing acircuit through conductor 363, springs 335, s rings 327, through thelower winding of re ay 301 to battery, energizing the relay 301. Relay301 upon energizing connects the private wiper 237 and conductor 362thru to the relay 303, energizing that relay from the ground picked upby the wiper 237 over circuit ineluding conductor 362, springs 321,spring 326 and its break contact, springs 338, interrupter spring-s 350,interrupter springs 349, through the conductor 370 the winding of relay303 to battery. The relay 303 energizes and again completes the circuitof the rotary magnet, since both of the private wipers of the finder FBhave encountered grounded contacts. Switching relay 302 is shortcircuited at this time, the u per terminal being connected to groundedre ease trunk conductor 369, and the lower terminal being connectedfirst through sprin 326 and its break contact and the normal y closedcontacts controlled by spring 321 through spring 333, conductor 363 tothe ground picked up by wiper 340 and then after relay 301 has energizedrelay 302 is short circuited over the circuit through spring 326 and itsbreak contact, 321 and its break contact, conductor 362 to the groundpicked up by the private wiper 237. 'Finder FB switches through afterthe fifth step has been taken, at which time the wiper 237 encountersthe contact to which conductor 258 is connected, and since that contactis ungrounded, the circuit of relay 303 is not completed and that relaystays deenergized to prevent the finder FB from taking another step.Since the line S is the only calling line at this instant, the contacton which wiper 240 is resting is grounded, and relay 301 is maintainedenergized by that ground. The control of the finder is therefore underthe control of wiper 237, which is engaging an ungrounded contact. Theabsence of ground on this wiper removes the short circuit from switchthrough relay 302 which energizes over circuit from grounded conductor369, through the winding of relay 302, spring 338 and its make contact,interrupter springs 350, interrupter springs 349, through the winding ofrelay 303 to battery. Relay 302 energizes in this circuit, but becauseof the high resistance of that relay relay 303 cannot energize. Relay302 upon energizing completes the loop circuit from the calling stationS to the first selector EB, that circuit being traceable from groundthrough the lower winding relay 309 of the. selector EB, through thespring 342 and its break contact, conductor 372, spring 331 and its makecontact, spring 324 and its make contact, conductor 365, wiper 238, nowengaging the contact to which" conduct-or 259 is connected, through thesubstation S1, conductor 257, wiper 236, conductor 361, spring 320 andits make contact, springs 325, conductor 368, spring 340 and its breakcontact, through the upper winding of relay 309 to battery. Theenergization of relay 302 also connects the private conductor 362 to therelease trunk conductor 369. The ground on the release conductor 369traverses a circuit through spring 326 and its make contact, spring 321and its make contact, conductor 362, wiper being old and well understoodby those skilled in the art is not shown in the drawings. The subscriberupon hearing dial tone manipulates his calling device to transmit thedigits of the Wanted party.

Finder distributor DB seeks another finder.

The energization of relay 302 of the finder FB closes springs 330,placing a ground upon conductor 374, completing a circuit from thatconductor through wiper 607, conductor 637, through the winding of relay603 to battery. Relay 603 upon energizing opens spring 627 to remove theground placed on the negative line conductor 368, through resistance, topermit the calling subscriber to operate the line relay of the selectorEB. Relay 603 opens springs 628 to open a point in the circuit of relay604, permitting that relay to fall back. Relay 604 upon falling backcloses spring 634, thereby closing a circuit from ground on oil normalspring 323 of the finder FB, conductor 373, wiper 605 now engaging thecontact to which that conductor is connected, conductor 441, spring634-, conductor 641, spring 623, interrupter spring 611, through thewinding of magnet 610 to battery, energizing the magnet 610 whichprepares to advance the wipers 605 to 609, inclusive, one step, and toopen interrupter springs 611 to open its own circuit. Magnet 610thereupon falls back, advancing the wipers 605 to 609, one step andreclosing its own circuit at interrupter spring 611. It the next finderin the group is busv. wiper 605 will again pick up ground potential,closing the above traced circuit for magnet 610 which will again beenergized preparatory to advancing the wipers another step. Magnet 610will operate in a buzzer like fashion, advancing the wipers 605 to 609step by step as long as the wiper 605 encounters grounded contactsassociated with busy finders. \Vhen the wipers encounter the contacts ofan idle finder, wiper 605 will fail to pick up ground, and the switchwill come to rest upon those contacts, thereby selecting that finder foruse.

All finders busy in group B.

In the event that the finder'FB happens to be the last idle finder ofthe group, when it is taken for use in the manner just described, andmoves off normal, the circuit for all finders busy relay 602 is openedfirst at springs 344 of selector EB and later at springs 339 of thefinder FB, that circuit including also conductor 367, spring 506 in itsbreak contact, conductor 434, spring 621, and the winding of relay 602.Relay 602 does not fall back immediately, because of the multipleholding circuits closed by the energization of relay 604 and includingspring 631, that circuit being maintained as long as relay 604 is in itsenergized position. When relay 604 dcenergizes, as pointed out above,relay 602 deenergizes, and at springs 623 opens a point in the testingcircuit of the allotter magnet 610, to prevent the finder allotter DBfrom needless rotation. At springs 622 and 624, relay 602 extends thestart circuit from the lines in group B to the group A controlequipment, to that during the interval that all finders in group B arebusy, calls originating in that group will be handled in group A in themanner pointed out hereinafter.

Operation of the key K1.

The operation of the key K1 in such a direction as to close springs 501,502 and 503, serves to cut out the control equipment comprising finderFA and finder allotter DA, and extends the start circuit from the groupA lines to the group B control equipment. The operation of the systemunder this circumstance is the same as it is in case all of the findersin group A are busy, that is all of the calls originating in both groupsof lines, are handled by the group B control equipment and finders.Calls from the group A line are handled by the group B finders, whichhave to take more than five steps to reach the contacts of those lines.Calls from the group B lines are handled by the group B finders whichtake not more than five steps to connect with the contacts of thoselines. It will, therefore, be appreciated that the operation ot thesystem when the key 1 is thrown in the direction indicated, is the sameas it would be it the all finders busy relay 404 were to becomedeenergized because of an all finders busy condition in the group A. Theoperation of the spring 501, to break its break contact and make itsmake contact, connects the conductor 260, leading from the resistanceunits associated with the vertical bank VA,

to the conductor 261, which is the corresponding conductor from thevertical bank VB In the event that the line S now initiates a call, theground placed on the conductor 250 in the manner hereinbefore describedtraverses a circuit through resistance 251, conductor 260, spring 501and its make contact, conductor 261, spring 505 and its break contact,conductor 511, through the winding of start relay 601 to battery,energizing that relay preparatory to starting, a group B finder insearch of the group A calling line. The operation of the spring 502,connects the busy common lead 161 of the group A to the busy common lead367 of the group B, so that the all finders busy relay 602 of the groupB is maintained energized over parallel circuits, the one leading fromground on spring 118 and its break contact of the selector EA, throughsprings 116, springs 114, off normal spring 126, conductor 161, spring.502 and its make contact, conductor 509, conductor 367, spring 506 andits break contact, conductor 434, spring 621 and its make contact,through the winding of relay 602 to battery, the other parallel pathbeing the one originating at spring 341 of the selector EB and extendingover the previously traced path to the relay 602. Thus it will be seenthat an idle finder in either group will maintain .this circuit of relay602 closed, so that that relay will remain energized, and controlequipment DB will be in a position to preselect that finder in readinessfor a call. The operation of spring 502 away from its break contact,disconnects the ground upon conductor 161, conductor 436, spring 435 andthe all finders busy relay 404, so that relay 404 deenergizes eventhough there may be an idle finder in the group A at the time. Theoperation of springs 503, shorts conductors 440 and 441 together, inmultiple with the short spaced across these conductors by springs 427 ofthe all finders busy relay 404. This additional short placed acrossthese conductors by springs 503 guards against the possibility of faultyoperation should the relay 404 fail to deenergize when its circuit isopen as explained above. It will be remembered that a multiple circuitfor relay 404 is closed thru springs 417 of the relay 402, so that inthe event that the control equipment DA was stuck and the relay 402 didnot deenergize, relay 404 would not be energized and consequentlysprings 427 would not be closed, however, springs 503 would accomplishtheir purpose. The deenergization of relay 442, responsive to theoperation of the key as explained above, removes ground from the lefthand half of the bank over which wiper 605 of the distributor DBrotates, to permit that distributor to select a finder in the group A.It will be noted that the banks of the distributor DB are divided in twohalves, the left hand being marked as A and the right hand as B.

The finders of the group A, such as finder FA, are multipled to the lefthand bank of the distributor DB, those multiples being omitted to avoidan unnecessary complication of the drawings. In this multiple, conductor165 would be connected to the bank contact a over which the wiper 606rotates, conductor 164 to the bank contact C over which conductor 607rotates, conductor 163 to the bank contact d over which wiper 608rotates and conductor 162 to the bank contact 6 over which wiper 609rotates. Assume now that all the finders in the group B are busy, andthat the finder FA is idle. The circuit of magnet 610 will be com letedas hereinbefore described from groun picked up by wiper 605 in the groupB of its bank, to rotate the wiper set 605-609 inclusive, over the groupB of contacts. When the wiper 605 reaches the contact a, it has passedout of the group B and is entering the group A. Since relay 404 hasdeenergized and removed ground from conductor 442, contact a will not begrounded. If the finder FA were busy, wiper 606, which is now engagingcontacts 6 to which conductor 165 of the finder FA is connected, wouldpick up a ground on that conductor, closing the circuit through thatwiper, conductor 440, spring 503 of the key K1 and springs 427 of therelay 404, in

multiple, to conductor 441, spring 634, spring I 623, conductor 640,interrupter spring 611, through the winding of magnet 610'to battery,energizing that magnet which prepares to advance the wipers andinterrupt its own circuit at spring 611 in the manner pointed outhereinbefore. Thus it will be seen that the wiper 606 of the distributorDB tests for finders in the group A, after the wipers of that switchhave encountered the contacts associated with that group. It is nowassumed that finder FA is idle, wiper 606 when it encounters contact bwill not pick up ground, and the finder DB will come to rest 7 upon thatcontact set, to preselect the finder FA for control by the controlequipment DB. Responsive to the energization of relay 601 by the line S,as pointed out hereinbefore, relay 604 is energized over the previouslytraced circuit, ground from spring 632 closes the circuit throughconductor 639, wiper 609, now engaging the contact e, conductor 162, tothe finder FA, that ground serving to operate the finder in the mannerhereinbefore pointed out.. When the finder FA switches through, spring135 places ground on conductor 164, which is connected to the contact 0on which wiper 607 is resting, that ground completes a circuit vthruthat wiper, conductor 637 to the relay 603, energizing that relay torelease the distributor DB from the finder FA, and to start it in searchof another idle finder in the manner hereinbefore pointed, out. Thedistributor DB will then search over the contacts of the group A, underthe control of ground picked up by wiper 606, stopping on the firstungroundcd contact to preselect that finder for use.

It will be noted that the last two contacts of the banks over whichwiper 605 rotates are permanently connected to ground. In other wordsthe capacity of the banks of the distributor DB is greater than thetotal number of finders in groups A and B. Unused contacts are connectedto permanent ground, so that when the wiper 605 encounters that contact,circuit of magnet 610 will again be closed and the finder DB will speedpast those contacts in search of an idle finder. If it is necessary toadd more finders to either group, this ground is removed, and the newfinders are connected to the contacts associated with that set.

Operation of key K1 to close springs 505 to 507 tnclucz'oe.

In a similar manner the operation of the key K1 to the right, to operatesprings 505,

506 and 507, removes the control equipment DB from service and divertsall calls originating in both line groups into the control equipment DA.The operation of spring 505 to close its make contact, connects theconductor 261 to the conductor 260, so that ground placed upon conductor252 by calling lines such as. S1 completes a circuit through theresistance 253, conductor 261, spring 505 and its make contact,conductor 260, spring 501 and its break contact, conductor 437, throughthe winding of relay 405 to battery, energizing that relay preparatoryto starting the control equipment DA to handle the call. The operationof spring 506, connects the busy common conductor 367 of the group Bthrough conductor 510, to the 'busy common conductor 161 of group A, sothat a ground placed on the busy common conductor 367 by an idle finderin the group B maintains the all finders busy relay 404 energized overcircuit from conductor 161 through spring 502 and its break contact,conductor 436, spring 425, through the winding of the relay,,404 tobattery. The operation of springs 507'closes a short between conductors431 and 432, for purposes to be hereinafter pointed out. Thedisconnection of spring 506 from its break contact, removes busy commonconductor 367 from conductor 434, thereby permitting the all findersbusy relay 602 to deenergize. The deenergization of relay 602, removesground from conductor 430, thereby removing ground from the B group ofcontacts in the bankover which wiper 415 rotates, to permit thedistributor DA to select a finder in the group B for use. The operationof the equipment DA is responsive to the encrgization of the relay andis the same as has been hereinbefore pointed out. When the wiper 415encounters the contact J, to which contact set the finder FD is assumedto be connected, it no longer finds ground, however, if the finder FD isbusy, wiper 414 will encounter a grounded contact. A multiple connectionis made between the left hand grou of contacts of the banks over whichtie wipers of- DA rotate and the finders of group B similar to thatexplained in connection with the distributor DB, it being sufficient atthis time to point out that the conductor 373 and the finder FB isconnected to contact 2' in the bank over which wiper 414 rotates,conductor 474 is connected with contact it over which the wiper 413rotates, conductor 475 is connected with bank contact 9 over which wiper412 rotates and the connector 376 is connected to the bank contact 7over which wiper 411 rotates. If finder ER is busy at the moment, wiper414 will pick up the ground from the off normal spring 323 of the finderFB, conductor 373, contact 2', wiper 414, conductor 431, through springs507 of the key K1 and springs 624 of the relay 602 and multiple,conductor 432, through springs 420, springs 427, conductor 445,interrupter springs 410, through the winding of magnet 401 to battery,energizing the magnet which interrupts its circuit at springs 410 andadvances the wipers of DA one step. When the finder FB is switchedthrough, relay 302 pulls up and places ground on conductor 374, thatground completing the circuit through contact h, wiper 413, conductor448, relay 403 to battery, energizing the relay 403 to release thecontrol equipment and causes the distributor DA to preselect anotheridle finder in the manner hereinbefore pointed out.

Operation of key K2.

In order that the equipment may be maintained in proper working order,it is necessary to frequently routine it, that is to cause the equipmentto perform a cycle of operations identical with the cycle performeddurmg the process of setting a call. In the present case, the finder FAand control equipment DA must be maintained in proper adjustment if itis to perform its function properly. For this purpose there is providedthe key K2, which may be termed an exercising key. When key K2 is thrownto close contacts 504, ground from those contacts completes a circuitover conductor 512, resistance 205 associated with the fifth contact inthe bank VA, conductor 260 the winding of relay 405 to battery. Relay405 energizes over this circuit to start the finder equipment in amanner hereinbefore pointed out. Finder FA, assuming that that finderhas been preselected by the distributor DA, therefore, starts steppingin a vertical direction. Since these exercising tests are usuallyperformed at the time of light traflic, it is correct to assume thatthere will be no calling lines in the group A, and that, therefore, thefinder will take five vertical steps before the vertical wi er 462encounters the grounded contact. The ground on conductor 512 places thefifth contact of VA at ground potential, so that when the wiper 262encounters it, the finder FA will be changed over from vertical torotary movement, and the rotary stepping will take place in the mannerhereinbefore described. Since it is assumedthere are no calling lines inthe group, all of the private contacts in the fifth level will begrounded and the finder FA will accordingly take eleven rotary steps, atthe end of which time the wipers of FA will be rotated oif of theirrespective banks. Private wipers 234 and 231 will, therefore, fail topick u ground, finder FA will be switched throug the distributor DA willpreselect another finder, and the control equipment will be released andrestored to normal as before. The finder switch after switching through,will not complete a loop circuit, consequently relay 102 of the selectorwill not be maintained energized, and it will restore and release theselector and finder by removing ground from the release conductor 151.The finder FA will, therefore, return to its normal position, and thenext finder of the group, having been preselected by the distributor DA,will be started as soon as relay 403 restores. The next finder of thegroup, will be put thru the same test, its wipers operated five verticalsteps and eleven rotary steps and then released. If a call should comein during this exercising test, the vertical wiper 262 will encounter agrounding contact prior to its arrival upon the fifth contact of thebank VA, consequently the finderwill rotate into that level, and stoupon the ungrounded private contacts associated with the calling line.The distributor will preselect another finder and the test willcontinuejust as if no interruptlon had occurred.

In a similar manner, the operation of key K2 to close spring 508, closesa circuit for the relay 601 of the distributor DB, causing thatdistributor to start the preselected finder, assumed to be the finderFB, which goes through a similar test. In this manner, the'switch roomattendant can place an exercising test upon all of the finders in thegroup, by simply throwing the exerelsing key first to close spring 504and then to close spring 508, he

may watch the operation of the finders and note the troubles which mayappear.

Supervision.

It will be noted that the energization of relay 402 of the controlequipment DA, responsive either to the initiation of a call by a line inthe group A, or by the operation of the exercising key, closes circuitfrom grounded springs 423, springs 430, conductor 443, throu h the lamp636 and to the slow alarm set in icated at the right of Fig. 6. Thisslow alarm set may be any well known timing device, which energizesafter a definite interval responsive to ground upon the conductor 443,to bring in a suitable alarm to call attention to the fact thatsomething is wrong in the finder equipment. In the normal course ofoperation of the system, relay 403 is ener ized res onsive to theswitching through 0 the fin er, before the slow alarm set has had timeto bring in the si nal. The lamp 636 is lighted each time a ca 1 is inprogress in the group A or the group B, serving to supervise thosecalls. The attendant. upon noting that the slow alarm set has operated,is called to the equipment, makes note of the trouble and takestemporary or permanent steps to remove it. Similarly the energization ofrelay 604 of the control equipment DB, closes the obvious circuitthrough springs 629 and 635 for the lamp 636 and the slow alarm set, theoperation being identical with that just pointed out.

It will also be noted that the deenergization of all finders busy relay404 closes a circuit through springs 428 for the all finders busy meter407, energizing that meter to register that all the finders of the grouphave been busy. Similarly the deenergization of all finders busy relay602 closes a circuit through spring 625 for all finders busy meter 611,to register that all the finders in group B have been busy. Theenergization of all finders busy meter 407 prepares at spring 424 acircuit for the lost call meter 406. Similarly the energization of allfinders busy meter 611 prepares another point in the circuit of the lostcall meter 406. If a call should be attempted during the time that bothof the control equipments have an all finders busy condition, groundupon the start conductor would energize either relay 405 or relay 601.Assume that relay 601 is energized, a circuit is then traceable fromground to springs 420, eonductor 439, conductor 508, spring 626,conductor 444, spring 424, winding of meter 406 to battery, energizingthat meter to register a lost call. The readings registered upon themeters 407 and 611 and upon the lost call meloo ter 406, are valuable toa trafiic department in determining whether or not the groups servedwhether it is necessary to rearrange some of the lines or to supply morefinders to the groups to handle the excessive traflic.

Supervision of the condition of the trunk lines from the finders to thefirst selector, is provided in the following manner. It will beremembered that in the detailed description of the operation of finder FA, after the wipers of that finder had been positioned upon the contactsof the calling line, relay 108 was switched through from a ground placedupon the release trunk conductor 151 by the first selector EA. In theevent that the first selector EA is at fault, and is not energizedresponsive to the placing of the ground upon fill conductor 163, aspointed out hereinbefore, this ground will not be present upon therelease trunk conductor 151 when it is needed to energize relay 108.Relay 403 of the control equipment DA cannot be energized until relay108 of the finder has energized and the circuit to the slow alarm setwill accordingly be maintained for a sufliciently long period to bringin an alarm. The attendant upon responding to the alarm, will determinewhich finder is in operation at the time and will note that the wipersare positioned upon the contacts of a calling line, and note that thefinder is not switched through, and thereby locate the trouble, eitherin the negative line conductor, in the line relay of the selector, or inthe release circuit.

Having thus described our invention, what we consider new and desire tohave protected by Letters Patent is pointed out in the appended claims.

What is claimed is:

1. In an automatic telephone system, a group of subscribers linesdivided into a plurality ot' subgroups, a start wire for each subgroup,a resistance for each start wire, a relay common to said group of lines,two groups of finders having access to said lines, means including adistributor for each group for preselecting an idle finder in eachgroup, an auxiliary start relay in each distributor, means responsive tothe initiation of a call on one of said lines for energizing said commonrelay over a circuit including the start wire and resistance individualto the subgroup containing said line, means controlled by said commonrelay for energizing the auxiliary start relay of the first of saiddistributors if that distributor has preselected an idle finder and forenergizing the auxiliary start relay of the other distributor if all thefinders of the first group are busy, and means responsive to theenergization of an auxiliary start relay for starting a preselectedfinder to find said calling line.

2. In an automatic telephone system, a group of subscribers lines, twogroups of finders having access to said lines, the order of access ofthe finders of one of said groups to said lines being the reverse ofthe. order of access of the finder of the other groups to the lines,means including a distributor for each group for preselect-ing an idlefinder in that group, two relays for said lines, one

" of said relays being associated with each of said distributors, meansresponsive to the initi ation of a call on one of said lines forenergizing one of said relays, means controlled by said energized relaythrough the associated distributor for starting a finder of the grouphaving first access to said line it there is an idle finder in thatgroup and for controlling the other distributor to start a finder of theother group if all of the finders of said first group are busy.

' 3. In an automatic telephone system, a group of subscribers linesdivided into subgroups, two finder switches having access to said lines,said switches having levels of contacts in which said lines terminate,means including multiple connections between said levels for giving thefirst of said switches access to said subgroups and lines in thesubgroups in one order and for giving the second of said switches accessto said subgroups and lines therein in the reverse order, and meansresponsive to the initiation of a call on one of said lines for startingthe finder having first aczxess to the subgroup containing that line toconnect with the line if that finder is idle and for starting the otherfinder if said first finder is busy.

4. In an automatic telephone system, two groups of subscribers lineseach divided into ten subgroups, two finder switches having access tosaid lines, each finder switch having two sets of wipers, said switcheshaving levels of contacts over which said wipers sweep and in which saidlines terminate a start wire for each finder, the start wire of thefirst finder extending to the first five subgroups of both of said linegroups and the start wire of the second finder extendin to the secondfive subgroups of both of sai line groups, a relay for each start wire,means responsive to the initiating of a call on one of said lines forenergizing one of said relays over the associated start wire to startthe finder associated therewith to find that line if that finder is idleand to start the other finder if said first finder is busy, and means inthe started finder for determining the wiper set to be used by thatfinder. I

5. In a telephone system, a group of lines divided into sub-groups, aplurality of finder switches having access to said lines, each finderhaving a plurality of contacts arranged in levels terminating saidlines, said levels of one of the finders bein connected to saidsubgroups of lines in a de nite order and the levels of another of thefinders being connected to said sub-groups in a reversed order, and saidcontacts in each level being connected to the sub-groups of said linesin a definite order in said first finder and in the reverse order insaid second finder.

6. In a telephone system, a plurality of subscribers lines divided intogroups each of which is divided into two sub-groups, a pair of finderswitches having access to all of said lines, a wiper set on said findersfor each of said sub-groups a starting relay individual to each group oflines, each relay responsive to a call from any line in its group tostart either of the finders, to select the line, means in the finderoperated after said line is selected for selecting the wiper setcorresponding to said group containing the line, and means forestablishing a connection through said wipers to said line.

7. In an automatic telephone system, a group of subscribers linesdivided into a plurality of subgroups, a start wire for each subgroup, aresistance for each start wire, two groups of finders having access tosaid lines,

means including adistributor for each group for preselecting an idlefinder in each group, an auxiliary start relay in each distributor,means responsive to the initiation olt'a call on one of said lines andcontrolled over a circuit including the start wire and resistanceindividual to the subgroup containing the calling line, for energizingthe auxiliary start relay of the-first of said distributors so thatdistributor has access to an idle finder, and for energizin theauxiliary start relay of the second distri utor if all the finders oi?the first group are busy, and means responsive to the energization of anauxiliary start relay for starting a preselected finder to find saidcalli line.

8. an automatic telephone system, a group of subscribers lines dividedinto subgroups, a plurality of'levels of contacts in each subgroup, aplurality of contacts in each of said levels, two coordinate finderswitches, banks for said switches, multiple connections between saidbanks for giving the second finder access to said levels and to thecontacts in each level in. reverse of the order of access of the firstfinder, means responsive to the initiation of a call on one of saidlines for registering a level digit and a contact digit in the bank ofeach of said finders, means controlled by said means for starting thefinder having the lowest level digit registered in its bank if thefinder is idle and for starting the other finder if said first finder isbusy, and means in said started finderi'or counting the level andcontact digits in sequence to bring that finder into en agement withsaid calling line.

11 witness whereof, I hereunto subscribe my name this 30th day of June,A. D. 1927. CLARENCE E. LOMAX. In witness whereof, I hereunto subscribemy name this 30th day of June A. D. 1927. r NORMAN H. SAUNDERS.

